Wide format printers are well known for printing large sized images onto a web of print media. They may be used, for example, in printing billboards or large office spreadsheets. Examples of popular wide format printers, which have been commercially available for many years, are the Hewlett Packard (HP) 1000/5000, the HP 3000/3500 and the Epson 7000/10 000.
All commercially available wide format printers have a moving printhead that traverses across a print medium whilst depositing ink. The print medium is necessarily stationary as the printhead traverses across it. When one line of an image has been printed the web incrementally advances ready for the next line to be printed.
An inherent disadvantage of current wide format printers is their slowness. High volume, high resolution printing is an objective that has been sought by the manufacturers of wide format printers for some time. Central to the problem of achieving high printing speeds is the ability to provide a printhead, which does not traverse across a stationary print medium and which is capable of generating the necessary number of ink dots at a suitable rate. Pagewidth printheads would avoid the need for a traversing printhead and allow high-speed printing. However, commercially available bubble jet and piezoelectric printheads suffer from excessive heat build up and energy consumption, and are therefore unsuitable for use in a pagewidth configuration. A number of disadvantages associated with such printheads are set out in U.S. Pat. No. 6,443,555.
The present Applicant has developed pagewidth printheads capable of producing images having a resolution as high as 1600 dpi. These printheads are manufactured using integrated circuit fabrication techniques. Details of these printheads are the subject of a number of granted US patents and pending US patent applications, which are listed in the cross reference section above.
The pagewidth printheads developed by the present Applicant are extremely suitable for use in wide format printers, because they can operate at high speeds and can be driven at an extremely high cyclical rate. Accordingly, the present Applicant has developed a wide format printer employing a pagewidth printhead. An example of such a wide format printer is described in U.S. Pat. No. 6,672,706 (Silverbrook), which is incorporated herein by reference. This printer makes high-speed wide format printing possible by “printing-on-the-fly”—that is, continuously feeding a web past the printhead and simultaneously printing without the web having to be stationary at any stage.
It will be appreciated that, in order to achieve “printing-on-the-fly” at high speed with consistent print quality, it is important that feeding of the web is finely controlled. Any variation in web speed or web tension will result in a deterioration in print quality in the form of, for example, a distorted image. Accordingly, it would be desirable to provide a feed mechanism which achieves substantially constant tension in a web as it passes a printhead.
It would be further desirable to avoid of slippage of the web relative to drive rollers in the feed mechanism in order to maintain a constant web speed. It would be further desirable to provide drive rollers having sufficient traction with the web to avoid slippage, but which also maintain this traction after repeated uses of the feed mechanism over long periods of time.
It would be further desirable to provide a feed mechanism which minimizes folding, creasing or crumpling of the web before it reaches a printhead.
It will also be appreciated that, in order to achieve “printing-on-the-fly” at high speed with consistent print quality, it is important that a constant distance is maintained between the printhead and the web onto which the printhead prints. Usually, inkjet printing is performed by printing onto a web in a print zone, with the web being supported by a platen. However, with pagewidth printheads secured to a metal carrier frame, there is a tendency for the metal frame to sag across its width relative to the platen. This sagging causes variation in the distance between the printhead and the web across the width of the printhead, which results in a deterioration in print quality. Accordingly, it would be desirable to provide a printhead arrangement, which minimizes any variation in distance between the printhead and the web.